1. Field of the Invention
The present invention concerns the manufacture of a long-haul optical communication line. A line of this kind may comprise 200 optical fibers each 20 km long connected in series, for example.
2. Description of the Prior Art
Commercially available fibers for this application are subject to chromatic dispersion at the wavelengths employed which distorts the signals transmitted.
If this dispersion is the only disturbing influence on the line the resulting distortion of the line output signal constitutes a primary distortion which is easily calculated, if this signal is defined, according to the length of the line fibers and their dispersion coefficients. Primary distortion of this kind can be exactly compensated by using dispersion compensating means causing chromatic dispersion opposite to that due to the line. In practise, however, dispersion is combined over the length of the line with non-linear effects such that dispersion compensating means can have only a limited efficiency, all the more so in that the chromatic dispersions of the fibers employed have a greater statistical spread. The resulting drawbacks include unacceptable transmission error rates and/or limitation of the throughput of information transmitted by the line.
Various arrangements are known in association with the use of dispersion compensating means to reduce these drawbacks.
One such arrangement is known from the document by D. Marcuse published in Journal of Lightwave Technology, vol. 9, No. 1, January 1991. This arrangement uses only fibers having a so-called "normal" dispersion which is relatively insensitive to the statistical spread of the chromatic dispersion. However, there remains some distortion due to this spread of the chromatic dispersion, mainly as the distance spanned by the link increases.
Another such arrangement retains only fibers whose chromatic dispersion is close to a given mean value. This arrangement is costly, however, because it wastes a number of fibers.
Another such arrangement classifies and connects the fibers in order of increasing chromatic dispersion as the amplitude of the optical wave conveying the signal to be transmitted decreases. This arrangement is described in the document by, D. Marcuse in Journal of Lightwave Technology, vol. 9, No. 3, March 1991.
The known arrangements are of limited effectiveness.
A particular object of the present invention is to provide in a simple and economical way a line enabling the previously mentioned drawbacks to be reduced.